The present invention relates generally to disc drives. More particularly the present invention relates to a pivot mechanism for a rotatable actuator in a hard disc drive (HDD) and a HDD that includes such a pivot mechanism.
In HDD""s rotary actuators are used to position magnetic transducers (heads) over selected information bearing tracks on the discs. The transducers have to be positioned with great precision by the servo-mechanism driving the actuators (usually a voice coil motorxe2x80x94VCM) which requires that the actuator should have a small frictional resistance to rotation along with no looseness or backlash due to clearances in the pivot bearings of the actuator. Such pivot bearings have been provided by two spaced sets of ball bearings housed in annular races which are mounted between a shaft, and a rotatable housing. The shaft is mounted on a base of the HDD and the actuator body is mounted on the housing. The bearing sets are pre-loaded so that each exerts a small axial force on the other to eliminate the internal clearances of the bearings. The pre-load force has to be adjusted carefully to provide adequate dynamic properties without increasing the frictional resistance to rotation (torque) of the assembly to an unacceptable extent. Nevertheless, this frictional torque is significant and lowering it as much as possible is highly desirable, particularly for high track density applications.
Another problem is that of cost. In HDD applications, higher quality ball bearings are required to assure proper (precision) servo-operation of the actuator. For example, a ball bearing of requisite quality will generally cost about one-third of the total cost of the pivot bearing arrangement. In order to stay competitive, HDD manufacturers continually seek lower cost design options.
U.S. Pat. No. 5,510,940 entitled xe2x80x9cBall Spindle for Reduced Friction Rotary Actuator in Disk Drivexe2x80x9d by T. A. Tacklind et al, granted Apr. 23, 1996, discloses a modified two bearing arrangement in which a further ball is associated with each of an upper and lower ball bearing set to support the rotary actuator of a disc drive. However whilst this may provide a reduced friction solution, it does not significantly reduce costs because two specialised ball bearing sets are still employed along with two additional balls.
U.S. Pat. No. 5,835,309 entitled xe2x80x9cPivot Bearingxe2x80x9d by Z. Boutaghou, granted Nov. 10, 1998, discloses another arrangement in which two freely rotating balls are mounted on the axis of rotation of an actuator and are axially separated, one at each axial end of the assembly. Each ball in this arrangement is confined by a moving concave bearing surface of the rotatable actuator and a corresponding fixed concave bearing surface of a fixed component. This structure, however, principally improves shock resistance but at the expense of increased friction because the area of contact between the balls and the concave bearing surfaces is increased compared with a conventional design using multiple balls in an annular race.
A need exists to provide a low friction bearing pivot mechanism for a rotary actuator in a disc drive at a low cost. The present invention meets this need and offers other advantages over the prior art.
The present invention relates to disc drives that have a pivot mechanism for the rotary actuator which meets the above mentioned need.
In accordance with one embodiment of the invention there is provided a disc drive which includes a base on which a drivable spindle is mounted. The drivable spindle carries at least one disc having a plurality of data storage tracks thereon. A rotatable actuator assembly is mounted on the base via a pivot mechanism and this assembly includes an actuator body and a transducer mounted on the actuator body which is positionable adjacent a data storage track on the disc on rotation of the actuator body. The pivot mechanism of the actuator assembly has a shaft mounted on the base and a housing, to which the actuator body is attached, rotatably mounted on the shaft. The mounting of the housing on the shaft is via an annular ball bearing set located near to the base end of the shaft and another bearing structure which is provided by co-acting surfaces of the shaft and the housing.
In another embodiment the invention provides a pivot mechanism as such for a rotatable actuator in a disc drive.
Preferably the bearing structure is provided by a convex surface on an end of the shaft or on the housing which engages a concave surface on the other of the housing or the shaft. Preferably the convex and concave surfaces are conical with the concave surface having a larger included angle than the convex surface. The included angle of the concave surface may be about 120xc2x0 and the included angle of the convex surface may be about 90xc2x0. The co-acting surfaces of the shaft and the housing may be such as to define a point bearing. Preferably the convex surface is on the shaft and the concave surface is on the housing.
These and various other features as well as advantages which characterize the present invention will be apparent upon reading of the following detailed description and review of the associated drawings.